The present invention relates to a pressure sensitive recording paper, particularly a novel dyestuff acceptor constituting a unit of a pressure sensitive recording paper in combination with techniques concerned with well known dyestuffs and pressure sensitive recording papers.
Pressure sensitive recording papers in the present invention are called as chemical recording papers or no carbon papers. As generally understood, the pressure sensitive recording papers mean all of such units as isolation of two or more materials being released by physical external force such as a pressure or change of a temperature, as the result those materials react each other to cause an optical change, more in detail change in absorption region of light or change in absorption intensity, and marking is effected in accordance with external forces.
Fundamentally, marking of pressure sensitive recording papers is effected by reacting a colorless or slightly colored dyestuff with a material capable of forming color of the dyestuff by a reaction therewith, namely a dyestuff acceptor, to form color. Dyestuffs in the present invention, as being understood from the following explanations, do not mean general dyestuffs in a broad sense, but mean materials which can form color by reacting with the dyestuff acceptor. The reaction means physiochemical adsorption as well as chemical reactions. Further, formation of color means such optical change as mentioned above. Heretofore, the most typical dyestuffs to be employed for pressure sensitive recording papers are Crystal violet lactone (hereinafter refered to as CVL) and benzoyl leucomethylene blue (hereinafter refered to as BLMB). Beyond them, many proton sensitive dyestuffs are known. Further, vanadium and iron containing compounds which color by forming complex compounds are known though they are essentially different from the above-mentioned dyestuffs.
Heretofore, as well known dyestuff acceptors, natural clay ores such as acid clay, bentonite, kaolinite and montmorillonite, inorganic materials such as finely powdered silicic anhydride, magnesium silicate and aluminum oxide and organic materials such as phenolic compounds, especially polyphenols, maleic resins and formaldehyde resins are known.
General pressure sensitive recording papers are composed of a microcapsule containing a dyestuff solution and a dyestuff acceptor which are coated on the surface or back surface of a paper, or a same surface, or at least one of which is made in the paper substance and the other is coated on the surface. The dyestuff solution and the dyestuff acceptor are isolated at least by shells of the microcapsules. When pressure is applied on the microcapsules in such a situation, capsules are raptured and isolation between the dyestuff solution and the dyestuff acceptor is released. As the result, the dyestuff contacts with the dyestuff acceptor and colors by a reaction, whereby marking is effected. Such mechanism or the producing technique of pressure sensitive recording papers are well known.
An object of the present invention is to provide pressure sensitive recording papers which form a bright and rich color, and can record such marking as not disappearing by influence of heat, light or water or not reducing density.
Another object of the present invention is to provide novel dyestuff acceptors which form stable and bright color by rapidly reacting with a dyestuff.